Method of producing a micro-actuator

ABSTRACT

In a method of producing a micro-actuator, a first adhesive is applied to a movable plate, and a movable electrode is placed on the first adhesive. A second adhesive is applied to the movable electrode, and a piezoelectric element is placed on the second adhesive. Next, a third adhesive is applied to an actuator base, a base electrode is placed on the third adhesive, and the third adhesive is semi-cured in the same manner as above. A fourth adhesive is applied to the base electrode, the piezoelectric element is placed on the fourth adhesive, and the fourth adhesive is semi-cured in the same manner as above. Finally, the adhered laminate thus obtained is placed into a heating furnace and heated at a predetermined temperature for a predetermined period of time to thereby fully cure the adhesives.

This is a divisional, of application Ser. No. 09/822,621, filed Mar. 30,2001 now U.S. Pat. No. 6,653,761.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a micro-actuator for fine movement of amagnetic head and to a method of producing the same.

2. Description of the Related Art

In recent years, reductions in size and thickness of magnetic diskdevices, a kind of external storage device for computers, have beenunder way and, further, reduction in electric power consumption isrequested. In addition, magnetic disk devices with higher recordingdensity and larger capacity are demanded. Larger capacity of themagnetic disk devices can generally be realized by increasing therecording capacity per disk. However, an increase in recording densitywithout changing the diameter of the disk leads to narrower track pitch;accordingly, the technical problem is how accurate the head device forreading and writing data on record tracks is positioned, and a headactuator with good positioning accuracy is desired.

Hitherto, in order to position a head with high accuracy in a magneticdisk device, generally, trials have been made to enhance rigidity ofmovable portions such as an actuator arm and raise the main resonancepoint frequency in in-plane directions. However, improvement ofresonance point has a limit, and even if the in-plane resonance point ofthe movable portion can be raised, there is still the problem thatvibration is generated due to spring characteristics of a bearingsupporting the movable portion, resulting in a reduction of positioningaccuracy.

As means for solving the above problem, a so-called two-stage actuatorin which a second actuator for following the tracks, namely, a trackingactuator is mounted on the tip of an arm of a head actuator, has beenproposed. The tracking actuator is for minutely moving the head providedat a tip portion of an arm, independently from motions of the headactuator, to achieve tracking of the head.

A two-stage actuator in which accurate positioning of the head isaccomplished by utilizing laminate type piezoelectric elements as thetracking actuator for the two-stage actuator has been proposed. Forexample, two laminate type piezoelectric elements are disposed on bothsides of an actuator arm, and a voltage is impressed in such a directionthat the piezoelectric element on one side is elongated while thepiezoelectric element on the other side shrinks, whereon the head isrotated in the direction of the piezoelectric element shrinking underthe impressed voltage.

However, in the two-stage actuator utilizing the laminate typepiezoelectric element according to the prior art, depolarization of thepiezoelectric element occurs due to impression of a voltage in thedirection reverse to the polarization direction of the piezoelectricelement, exposing of the piezoelectric element to a high-temperatureatmosphere, aging or the like; as a result, displacement per unitvoltage gradually diminishes. Therefore, there is the problem that whenthe system is used for a certain long time, a desired stroke cannot beobtained. Furthermore, the two-stage actuator according to the prior artutilizing the laminate type piezoelectric elements has the disadvantagethat productivity of the laminate type piezoelectric elements is bad,and high accuracy or precision of outer sizes of the elements isrequired, leading to high cost.

Two-stage actuators utilizing a shearing type piezoelectric element inplace of the laminate type piezoelectric element having theabove-mentioned many problems have been proposed in Japanese PatentLaid-open No. Hei 10-293979 and Japanese Patent Laid-open No. Hei11-31368. A minute moving mechanism for head disclosed in the JapanesePatent Laid-open No. Hei 11-31368 has a three-layer structure in whichtwo shearing type piezoelectric elements having different polarizationdirections are mounted on an electrode formed at the tip of a head arm,and a head suspension is mounted thereon through a movable membertherebetween.

Therefore, this structure has a larger thickness from the head arm tothe suspension, as compared with the conventional structure in which thesuspension is fitted to the head arm with only a spacer. Thus, thetwo-stage actuator with the three-layer structure is unsuitable forreduction in thickness of the head actuator. Further, the increasedthickness leads to greater distance between disk surfaces, whereby thenumber of disks mountable in the disk device is decreased, and storagecapacity is also decreased as compared with the conventional disk devicehaving the same height.

A minute moving mechanism for head which solves the above-mentionedproblems has been proposed by the present applicant. In the invention ofthe previous application, an actuator base bent in a crank shape isfixed to a tip portion of an actuator arm. A base electrode, a shearingtype piezoelectric element, a movable electrode and a movable plate arelaminated and fixed on the actuator base, and a suspension is fixed tothe movable plate. With the actuator base bent in a crank shape, the topsurface of the actuator base and the top surface of the movable platecan be flush with each other, so that the minute moving mechanism forhead utilizing the shearing type piezoelectric element can be madethinner.

In the invention of the previous application, electrical conduction mustbe provided between the shearing type piezoelectric element and the baseelectrode and the movable electrode, and, therefore, the base electrodeand the movable electrode have been fixed to the piezoelectric elementby use of a conductive adhesive. On the other hand, electricalinsulation must be kept between the actuator base and the base electrodeand between the movable electrode and the movable plate, and, therefore,fixation between the actuator base and the base electrode and betweenthe movable electrode and the movable plate has been made by use of anordinary insulating adhesive.

In the method of producing a micro-actuator using a conductive adhesiveand an ordinary insulating adhesive according to the invention of theprevious application, it is needed to selectively use the two types ofadhesive, which leads to complicated production steps. Further, use of aconductive adhesive may easily be attended by generation of ashort-circuit due to a mistake in production process. Thus, it iscontemplated to contrive use of a single adhesive by using an insulatingadhesive also for adhesion of the electrode and the piezoelectricelement. However, where an adhesive is merely applied and cured, anadhesive layer thin enough to obtain electrical connection cannot beformed.

Therefore, a method of applying a pressure at the time of curing theadhesive is contemplated. However, where pressure is merely applied uponeach lamination of component parts through an adhesive, the thickness ofthe adhesive layer on application of pressure is added to the thicknessof component parts, so that variations of the thickness of the componentparts will come out as large variations of the total thickness. Further,where electrical connection is envisioned, two shearing typepiezoelectric elements are mounted on the base electrode, and thedifference between the thicknesses of left and right piezoelectricelements may cause variations of the adhesive layer even if they arepressed in the same manner.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod of producing a micro-actuator using a method of adhesion capableof securely providing electrical connection as required, irrespectivelyof variations of component parts.

It is another object of the present invention to provide amicro-actuator capable of selectively providing electrical connectionand electrical insulation as required while using the same adhesive.

In accordance with an aspect of the present invention, there is provideda method of producing a micro-actuator, comprising the steps of:applying a first adhesive to a movable plate; placing a movableelectrode on the first adhesive; clamping the movable plate and themovable electrode between a first stage and a first head, followed byheating for a first predetermined period of time while exerting a firstpredetermined press load onto the first head to semi-cure the firstadhesive; applying a second adhesive to the movable electrode; placing apiezoelectric element on the second adhesive; clamping the movableplate, the movable electrode and the piezoelectric element between thefirst stage and a second head, followed by heating for a secondpredetermined period of time while exerting a second predetermined pressload onto the second head to semi-cure the second adhesive; applying athird adhesive to an actuator base; placing a base electrode on thethird adhesive; clamping the actuator base and the base electrodebetween a second stage and a third head, followed by heating for a thirdpredetermined period of time while exerting a third predetermined pressload onto the third head to semi-cure the third adhesive; applying afourth adhesive to the base electrode; placing the piezoelectric elementon the fourth adhesive; and clamping the actuator base, the baseelectrode, the piezoelectric element, the movable electrode and themovable plate between the second stage and a fourth head, followed byheating for a fourth predetermined period of time while exerting afourth predetermined press load onto the fourth head to semi-cure thefourth adhesive.

Preferably, the first to fourth adhesives comprise a thermo-settingepoxy resin. Further preferably, the first to fourth adhesives areapplied by use of a plurality of pins.

In accordance with another aspect of the present invention, there isprovided a method of producing a micro-actuator, comprising the stepsof: applying a first adhesive to a movable plate; placing a movableelectrode on the first adhesive; clamping the movable plate and themovable electrode between a first stage and a first head, followed byheating for a first predetermined period of time while exerting a firstpredetermined press load onto the first head to semi-cure the firstadhesive; applying a second adhesive to an actuator base; placing a baseelectrode on the second adhesive; clamping the actuator base and thebase electrode between a second stage and a second head, followed byheating for a second predetermined period of time while exerting asecond predetermined press load onto the second head to semi-cure thesecond adhesive; applying a third adhesive to the base electrode;placing a piezoelectric element on the third adhesive; clamping theactuator base, the base electrode and the piezoelectric element betweenthe second stage and a third head, followed by heating for a thirdpredetermined period of time while exerting a third predetermined pressload onto the third head to semi-cure the third adhesive; applying afourth adhesive to the piezoelectric element; placing the movableelectrode on the fourth adhesive; and clamping the actuator base, thebase electrode, the piezoelectric element, the movable electrode and themovable plate between the second stage and a fourth head, followed byheating for a fourth predetermined period of time while exerting afourth predetermined press load onto the fourth head to semi-cure thefourth adhesive.

In accordance with a further aspect of the present invention, there isprovided a micro-actuator comprising: an actuator base; a base electrodeadhered to the actuator base by a first adhesive; first and secondshearing-type piezoelectric elements having polarization directionsopposite to each other and perpendicular to the element thicknessdirection, adhered to the base electrode by a second adhesive; a movableelectrode adhered to the first and second piezoelectric element by athird adhesive; and a movable plate adhered to the movable electrode bya fourth adhesive, wherein the second and third adhesives are thinenough to allow electrical conduction respectively between the first andsecond piezoelectric elements and the base electrode and between thefirst and second piezoelectric elements and the movable electrode; andthe first and fourth adhesives are thick enough to provide electricalinsulation respectively between the actuator base and the base electrodeand between the movable plate and the movable electrode.

Preferably, the first to fourth adhesives comprise a thermo-settingepoxy resin, and the second and third adhesives have a thickness of notmore than 3 μm.

In accordance with a still further aspect of the present invention,there is provided a method of producing a micro-actuator, comprising thesteps of: applying a first adhesive to an actuator base; placing a baseelectrode on the first adhesive; clamping the actuator base and the baseelectrode between a first stage and a first head, followed by heatingfor a first predetermined period of time while exerting a firstpredetermined press load onto the first head to semi-cure the firstadhesive; applying a second adhesive to the base electrode; placing apiezoelectric element on the second adhesive; clamping the actuatorbase, the base electrode and the piezoelectric element between the firststage and a second head, followed by heating for a second predeterminedperiod of time while exerting a second predetermined press load onto thesecond head to semi-cure the second adhesive; applying a third adhesiveto the piezoelectric element; placing a movable plate on the thirdadhesive; and clamping the actuator base, the base electrode, thepiezoelectric element and the movable plate between a second stagehaving a first suction hole and a third head having a second suctionhole, followed by heating for a third predetermined period of time whiledrawing under vacuum through the first and second suction holes andexerting a third predetermined press load onto the third head tosemi-cure the third adhesive.

In accordance with a still further aspect of the present invention,there is provided a micro-actuator comprising: an actuator base; a baseelectrode adhered to the actuator base by a first adhesive; first andsecond shearing-type piezoelectric elements having polarizationdirections opposite to each other and perpendicular to the elementthickness direction, adhered to the base electrode by a second adhesive;a movable plate adhered to the first and second piezoelectric elementsby a third adhesive; a first wire for connecting the first and secondpiezoelectric elements; and a second wire for connecting either one ofthe first and second piezoelectric elements to the base electrode,wherein the base electrode comprises a first conductor patternelectrically connected to the first and second piezoelectric elementsthrough the second adhesive, and a second conductor pattern electricallyindependent from the first conductor pattern and connected to the secondwire, the second adhesive is thin enough to allow electrical conductionbetween the base electrode and the first and second piezoelectricelements, and the first and third adhesives are thick enough to provideelectrical insulation respectively between the actuator base and thebase electrode and between the movable plate and the first and secondpiezoelectric elements.

Preferably, the second adhesive comprises a thermo-setting epoxy resin,and has a thickness of not more than 3 μm.

In accordance with a still further aspect of the present invention,there is provided a method of adhering a plurality of members,comprising the steps of: applying a first adhesive to a first member;placing a second member on the first adhesive; clamping the first andsecond members between a first stage and a first head, followed byheating for a first predetermined period of time while exerting a firstpredetermined press load onto the first head to semi-cure the firstadhesive; applying a second adhesive to the second member; placing athird member on the second adhesive; and clamping the first member, thesecond member and the third member between the first stage and a secondhead, followed by heating for a second predetermined period of timewhile exerting a second predetermined press load onto the second head tosemi-cure the second adhesive.

The above and other objects, features and advantages of the presentinvention and the manner of realizing them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claims with reference to the attacheddrawings showing some preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a two-stage actuator utilizing a piezomicro-actuator according to the present invention;

FIG. 1B is a side view of the same;

FIG. 2 is an exploded perspective view of a piezo micro-actuatoraccording to a first embodiment of the invention;

FIG. 3A is a side view of a head assembly adopting the piezomicro-actuator according to the first embodiment;

FIG. 3B is a plan view of the same;

FIGS. 4A to 4D are views illustrating a method of producing the piezomicro-actuator according to the first embodiment;

FIG. 5 is a view showing the size relationships of a third head;

FIG. 6 is a view showing the shape of a transfer pin;

FIG. 7A is a view showing the position of transferring an adhesive to abase electrode;

FIG. 7B is a view showing the position of transferring an adhesive to amovable electrode;

FIG. 7C is a view showing the position of transferring an adhesive to apiezoelectric element;

FIG. 8 is a diagram showing the relationship between the number of timesof successive transfer and transfer diameter of an adhesive;

FIG. 9 is a diagram showing the relationship between the number of timesof successive transfer and coating weight of an adhesive;

FIG. 10 is a schematic enlarged sectional view of a piezo micro-actuatorafter component parts are adhered;

FIGS. 11A to 11D are views showing another method of producing the piezomicro-actuator according to the first embodiment;

FIG. 12 is a view showing the size relationships of a fifth head;

FIG. 13 is an exploded perspective view of a piezo micro-actuatoraccording to a second embodiment of the invention; and

FIGS. 14A to 14C are views illustrating a method of producing the piezomicro-actuator according to the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, embodiments of the present invention will be described in detailreferring to the drawings. Referring to FIG. 1A, there is shown a planview of a two-stage head actuator adopting a piezo micro-actuator of theinvention as a tracking actuator. FIG. 1B is a side view of the same.

Numeral 2 denotes the two-stage head actuator comprised of an actuatorassembly 4 and a magnetic circuit (not shown). The actuator assembly 4is rotatably fitted on a shaft 6 fixed to a base (not shown) of amagnetic disk device. The actuator assembly 4 comprises an actuatorblock 8 rotatably fitted to the shaft 6 through a bearing 7, a pluralityof actuator arms 10 formed as one body with the actuator block 8 andextended in one direction, and a coil support member 12 extended in adirection opposite to the actuator arms 10.

A flat coil 14 is supported on the coil support member 12, and themagnetic circuit (not shown) fixed to a base of the magnetic disk deviceand the coil 14 inserted in a gap of the magnetic circuit constitute avoice coil motor (VCM). A piezo micro-actuator 16 according to theinvention is fitted to a tip portion of each of the actuator arms 10,and a base end portion of a suspension 18 is fixed to the piezomicro-actuator 16. A tip portion of the suspension 18 supports amagnetic head 20.

Referring to FIG. 2, there is shown an exploded perspective view of apiezo micro-actuator 16 according to a first embodiment of theinvention. A fixing portion 22 a of an actuator base 22 is fixed byinserting a caulking projection 22 d formed as one body with the fixingportion 22 a into a caulking hole 10 a bored in the actuator arm 10,followed by caulking. The actuator arm 10 is grounded. A tip portion 22c of the actuator base 22 is formed lower than the fixing portion 22 awith a step portion 22 b therebetween, and a pair of shearing typepiezoelectric elements 28 a, 28 b clamped between a base electrode 24and a movable electrode 26 are mounted on the tip portion 22 c. The pairof shearing type piezoelectric elements 28 a, 28 b have polarizationdirections opposite to each other and perpendicular to the elementthickness direction. The polarization directions are parallel to thelongitudinal direction of the actuator arm 10.

The base electrode 24 is provided with a tab (wiring lead portion) 25projected sideways from the tip portion 22 c of the actuator base 22.Similarly, the movable electrode 26 is provided with a tab 27 projectedsideways from the tip portion 22 c of the actuator base 22. A movableplate 30 has a base portion 36, defined by a first notch 32 and a secondnotch 34, and a movement amount enlarging portion 38. The base portion36 of the movable plate 30 is fitted to the movable electrode 26, andthe suspension 18 is fixed to the movement amount enlarging portion 38of the movable plate 30 by spot welding or the like. Numeral 40 denotesa relay FPC fitting portion provided on a side of the base end portionof the suspension 18.

Referring to FIG. 3A, there is shown a side view of a head assemblyadopting the piezo micro-actuator 16 according to the first embodiment.FIG. 3B is a plan view of the same. As shown in FIG. 3A, when the piezomicro-actuator 16 is assembled, the tab 25 of the base electrode 24 andthe tab 27 of the movable electrode 26 are disposed adjacent to eachother. As a result, soldering of a relay FPC 42 provided with leadpatterns 43, 45 for the tabs 25, 27 becomes easy, and it is easy toapply a voltage to the base electrode 24 and the movable electrode 26.

Next, referring to FIGS. 4A to 4D, a first method of producing the piezomicro-actuator according to the first embodiment of the presentinvention will be described. First, as shown in FIG. 4A, the movableplate 30 is mounted on a first stage 44 having a flat top face, and afirst adhesive 46 comprising a thermo-setting epoxy resin is applied tothe movable plate 30. Next, the movable electrode 26 is mounted on thefirst adhesive 46. A first head 48 is mounted on the first stage 44,thereby clamping the movable plate 30 and the movable electrode 26between the first stage 44 and the first head 48. The first head 48 hasa groove 49 having a depth H1=152 μm.

The first head 48 incorporates a heater, and is heated to about 120° C.The first stage 44 is mounted on a heating plate and is heated whileexerting a predetermined press load, for example, about 43 Newtons tothe first head 48. The first stage 44 was heated up to 120° C. afterabout 90 seconds, and maintained at that temperature for 120 seconds,whereby the first adhesive 46 was semi-cured. Next, a second adhesivecomprising a thermo-setting epoxy resin is applied to the movableelectrode 26, and a pair of piezoelectric elements 28 a, 28 b aremounted on the second adhesive.

Next, as shown in FIG. 4B, the second adhesive was heated and semi-curedwhile exerting a press load of 43 Newtons to a second head having agroove 51 having a depth H2=290 μm. In the same manner as the step shownin FIG. 4A, the adhesive curing temperature was 120° C. and the heatingtime was 210 seconds. In the pressing step shown in FIG. 4B, the firstadhesive 46 formed somewhat thicker can be utilized as a cushion and,therefore, variations in the height of the piezoelectric elements 28 a,28 b can be absorbed by sinking of the first adhesive 46. Further, bysetting the depth H2 of the groove 51 at an appropriate value asmentioned above, the second adhesive can be formed very thin to have athickness of not more than 3 μm, and electrical connection can besecured between the movable electrode 26 and the piezoelectric elements28 a, 28 b.

Next, as shown in FIG. 4C, the actuator base 22 is mounted on a secondstage 52 having a groove 54. The depth of the groove 54 is 220 μm. Athird adhesive 56 also comprising a thermo-setting epoxy resin isapplied to the actuator base 22, and the base electrode 24 is placed onthe third adhesive 56. A third head 58 is mounted on the second stage 52to clamp the actuator base 22 and the base electrode 24 between thesecond stage 52 and the third head 58. As shown in FIG. 5, the thirdhead 58 has a pair of end projections 58 a and a central projection 58b, and height difference H3 between the end projections 58 a and thecentral projection 58 b is 50 μm. The third adhesive 56 was heated andsemi-cured while exerting a press load of 43 Newtons onto the third head58. The adhesive curing temperature and heating time were the same as inthe step shown in FIG. 4A; namely, the adhesive curing temperature was120° C. and the heating time was 210 seconds.

Next, a fourth adhesive also comprising a thermosetting epoxy resin isapplied to the base electrode 24. Further, as shown in FIG. 4D, thelaminate or adhered body obtained in the step of FIG. 4B is inverted,and the piezoelectric elements 28 a, 28 b are mounted on the fourthadhesive. A fourth head 60 is mounted on the second stage 52 to clampthe actuator base 22, base electrode 24, piezoelectric elements 28 a, 28b, movable electrode 26 and movable plate 30 between the second stage 52and the fourth head 60. The fourth head 60 has a groove 61 having adepth H4=200 μm.

The fourth adhesive was semi-cured by heating a predetermined period oftime while exerting a press load of 43 Newtons on the fourth head 60.The adhesive curing temperature and heating time were the same as in thestep of FIG. 4A; namely, the adhesive curing temperature was 120° C. andheating time was 210 seconds. In the step shown in FIG. 4D, the thirdadhesive 56 formed somewhat thicker can be utilized as a cushion and,therefore, thickness variations of component parts can be absorbed.Further, by setting the depth H4 of the groove 61 at an appropriatevalue mentioned above, the fourth adhesive can be formed very thin tohave a thickness of not more than 3 μm, and it is possible to secureelectrical connection between the base electrode 24 and thepiezoelectric elements 28 a, 28 b. Finally, the adhered laminateobtained in FIG. 4D was placed into a heating furnace, and heated at120° C. for about 30 minutes, whereby the first to fourth adhesives werefully cured.

In order to control the amount of adhesives applied to component parts,application of the adhesives was carried out by a pin transfer system inwhich a plurality of transfer pins 64 as shown in FIG. 6 were used. Eachof the pins has a diameter of 0.49 mm. The plurality of transfer pins 64shown in FIG. 6 are pressed against an adhesive layer extended by asqueezee to a thickness of 100 to 150 μm, thereby applying the adhesiveto the transfer pins 64. The transfer pins 64 are pressed againsttransfer positions shown by circles in FIGS. 7A to 7C, thereby applyingthe adhesive to component parts. The adhesive is applied to the baseelectrodes 24 at five points as shown in FIG. 7A, is applied to themovable electrode 26 at four points as shown in FIG. 7B, and is appliedto the piezoelectric element 28 a or 28 b at two points as shown in FIG.7C. In fact, the adhesive is applied to the actuator base 22 in place ofthe base electrode 24, is applied to the movable plate 30 in place ofthe movable electrode 26, and is applied to the movable electrode 26 andthe base electrode 24 in place of the piezoelectric element 28 a, 28 b.

Referring to FIG. 8, there is shown the relationship between the numberof times of successive transfer and transfer diameter of the adhesive.Although there are some dispersions, the pin transfer system provides atransfer diameter of about 700 μm. Referring to FIG. 9, there are shownthe relationship between the number of times of successive transfer andcoating weight of the adhesive. As is clear from FIG. 9, the adhesivecan be stably applied with a coating weight of 0.016 mg for not lessthan 250 times, excepting the first several tens of times.

Referring to FIG. 10, there is shown an enlarged sectional view of anadhered laminate after adhesion of component parts. As has beendescribed above, the second adhesive 47 and the fourth adhesive 57 havea thickness of not more than 3 μm and, therefore, electrical conductioncan be secured between the movable electrode 26 and the piezoelectricelement 28 a and between the base electrode 24 and the piezoelectricelement 28 a. In addition, since the first adhesive 46 and the thirdadhesive 56 have a sufficient thickness, insulation can be providedbetween the movable plate 30 and the movable electrode 26 and betweenthe actuator base 22 and the base electrode 24.

Next, referring to FIGS. 11A to 11D, another method or a second methodof producing the piezo micro-actuator according to the first embodimentof the invention will be described. The step shown in FIG. 11A is thesame as the step shown in FIG. 4A, and the description thereof isomitted. Further, the step shown in FIG. 11B is the same as the stepshown in FIG. 4C, and the description thereof is omitted.

According to the method in this embodiment, as shown in FIG. 1C, thepiezoelectric elements 28 a, 28 b are adhered to the base electrode 24.Namely, a third adhesive is applied to the base electrode 24, and thepiezoelectric elements 28 a, 28 b are mounted thereon. Next, a fifthhead 64 is mounted on the second stage 52 to clamp the actuator base 22,base electrode 24 and piezoelectric elements 28 a, 28 b between thesecond stage 52 and the fifth head 64. As shown in FIG. 12, the fifthhead 64 has a pair of end projections 64 a and a central projection 64b, and the height difference H5 between the end projections 64 a and thecentral projection 64 b is 90 μm.

The third adhesive was semi-cured by heating at 120° C. for 210 secondswhile exerting a press load of 43 Newtons to the fifth head 64. Bysetting the value of H5 at an appropriate value as mentioned above, thethird adhesive can be formed very thin to have a thickness of not morethan 3 μm, and electrical connection can be secured between the baseelectrode 24 and the piezoelectric elements 28 a, 28 b. Further, in thepressing step of FIG. 11C, the third adhesive 56 formed to be somewhatthicker can be utilized as a cushion and, therefore, the difference inthickness between the piezoelectric elements 28 a, 28 b can be absorbed.

The step shown in FIG. 11D is the same as the step shown in FIG. 4D and,therefore, description thereof is omitted. In the second method ofproduction also, the laminate obtained in FIG. 11D was placed in aheating furnace, followed by heating at 120° C. for about 30 minutes tofully cure the adhesives. The first and second methods differ from eachother in that the piezoelectric elements 28 a, 28 b are first adhered tothe movable electrode 26 as shown in FIG. 4B in the first method,whereas the piezoelectric elements 28 a, 28 b are first adhered to thebase electrode 24 as shown in FIG. 11C in the second method.

When the piezo micro-actuator was produced by the first method ofproduction, the yield was about 92%. Because the heating time is long,16 pieces of each of the component parts of the piezo micro-actuatorwere joined into a sheet, and 16 pieces of piezo micro-actuators wereproduced at a time, to shorten the production time. The yield wassimilar to the above-mentioned percentage. In this case, the press loadwas 16 times of the value in the case of producing one piezomicro-actuator at a time, namely, about 680 Newtons, and the heatingtemperature and heating time period were the same as above. Since 16sets were processed at a time, the heating time per set could beshortened to about 13 seconds. Since the application of adhesives wascarried out by the pin transfer system, 16 sets could be processed at atime, and process time could be shortened as compared with a dispensingsystem.

Referring to FIG. 13, there is shown an exploded perspective view of apiezo micro-actuator according to a second embodiment of the invention.A base electrode 24′ is adhered to an actuator base 22. The baseelectrode 24′ has a large first conductor pattern 24 a and a small-areasecond conductor pattern 24 b independent from the first conductorpattern 24 a. A pair of shearing type piezoelectric elements 28 a, 28 bare adhered to the base electrode 24′. The pair of piezoelectricelements 28 a and 28 b are bonding-connected by a first wire 68, whilethe piezoelectric-element 28 a and the second conductor pattern 24 b ofthe base electrode 24′ are bonding-connected by a second wire 70.

A movable plate 30 is adhered to the piezoelectric elements 28 a, 28 b.A suspension 18′ is fixed to the movable plate 30 by spot welding or thelike. In the piezo micro-actuator 16′ of this embodiment, the movableelectrode 26 in the first embodiment is omitted, and the pair ofpiezoelectric elements 28 a, 28 b are connected to the conductor pattern24 b of the base electrode 24′ by the two wires 68, 70.

Referring to FIGS. 14A to 14C, a method of producing the piezomicro-actuator 16′ according to the second embodiment will be described.First, as shown in FIG. 14A, the base electrode 24′ is adhered to theactuator base 22 by a third adhesive 56. The pressing step of FIG. 14Ais the same as the step of FIG. 11B and, therefore, description thereofis omitted. Next, as shown in FIG. 14B, the piezoelectric elements 28 a,28 b are adhered to the base electrode 24′ by a second adhesive. Thepressing step of FIG. 14B is the same as the step of FIG. 11C and,therefore, description thereof is omitted.

Next, the adhered laminate obtained in FIG. 14B is mounted on a thirdstage 72 having a suction hole 76, as shown in FIG. 14C. Like the secondstage 52, the third stage 72 has a groove 74 having a depth of 220 μm.An adhesive 78 comprising a thermo-setting epoxy resin is applied to thepiezoelectric elements 28 a, 28 b by pin transfer, and a movable plate30 is placed on the adhesive 78. Then, a sixth head 80 having a suctionhole 82 is mounted on the third stage 72 to clamp the actuator base 22,base electrode 24, piezoelectric elements 28 a, 28 b and movable plate30 between the third stage 72 and the sixth head 80. Like the fourthhead 60, the sixth head 80 has a groove 81 having a depth H4.

The adhesive 78 was semi-cured by heating at 120° C. for 210 secondswhile drawing under vacuum through the suction holes 76, 82 of the thirdstage 72 and the sixth head 80 and exerting a predetermined press load,namely a press load of 43 Newtons, to the sixth head 80. Heating andpressing while drawing under vacuum on the upper and lower sides is forsecuring the thickness of the adhesive 78. By this, a layer of theadhesive 78 with a thickness of about 20 μm can be formed. Then, thelaminate obtained in FIG. 14C was placed in a heating furnace, followedby heating at 120° C. for about 30 minutes to thereby fully cure theadhesives.

Because the heating time is long, 16 pieces of each of component partsof the piezo micro-actuator 16′ were joined into a sheet, and 16 piecesof the piezo micro-actuators 16′ were produced at a time, therebyshortening production time. The yield was about 92%, the same as that inthe case of producing the piezo micro-actuator one by one. The pressload was 16 times that in the case of producing the piezo micro-actuatorone by one, namely about 680 Newtons, and the heating temperature andheating time were the same as above. Since the 16 sets were processed ata time, the heating time per set could be shortened to about 13 seconds.Because the application of adhesive was carried out by the pin transfersystem, 16 sets could be treated at a time, and production time could beshortened as compared with a dispensing system.

As is clear from the embodiments described above, the present inventionis characterized in the method of adhering component parts or memberswhile controlling the thickness of adhesive layers. While the abovedescription has been made referring to an example of applying theadhesion method of the invention to production of a piezomicro-actuator, the present invention is not limited to the example, andcan be applied to a method of adhering a plurality of members.

As has been detailed above, by controlling the thickness of adhesivelayers according to the invention, it is possible to provide electricalconnection and electrical insulation as required while using the sameinsulating adhesive, and to produce a micro-actuator with high yield.

1. A method of producing a micro-actuator, comprising the steps of:applying a first adhesive to a movable plate; placing a movableelectrode on said first adhesive; clamping said movable plate and saidmovable electrode between a first stage and a first head, followed byheating for a first predetermined period of time while exerting a firstpredetermined press load onto said first head to semi-cure said firstadhesive; applying a second adhesive to said movable electrode; placinga piezoelectric element on said second adhesive; clamping said movableplate, said movable electrode and said piezoelectric element betweensaid first stage and a second head, followed by heating for a secondpredetermined period of time while exerting a second predetermined pressload onto said second head to semi-cure said second adhesive; applying athird adhesive to an actuator base; placing a base electrode on saidthird adhesive; clamping said actuator base and said base electrodebetween a second stage and a third head, followed by heating for a thirdpredetermined period of time while exerting a third predetermined pressload onto said third head to semi-cure said third adhesive; applying afourth adhesive to said base electrode; placing said piezoelectricelement on said fourth adhesive; and clamping said actuator base, saidbase electrode, said piezoelectric element, said movable electrode andsaid movable plate between said second stage and a fourth head, followedby heating for a fourth predetermined period of time while exerting afourth predetermined press load onto said fourth head to semi-cure saidfourth adhesive.
 2. A method of producing a micro-actuator as set forthin claim 1, wherein said first to fourth adhesives comprise athermo-setting epoxy resin.
 3. A method of producing a micro-actuator asset forth in claim 1, wherein said first to fourth adhesives are appliedby use of a plurality of pins.
 4. A method of producing a micro-actuatoras set forth in claim 1, further comprising the step of heating theadhered laminate at a predetermined temperature for a fifthpredetermined period of time to fully cure said first to fourthadhesives.
 5. A method of producing a micro-actuator, comprising thesteps of: applying a first adhesive to a movable plate; placing amovable electrode on said first adhesive; clamping said movable plateand said movable electrode between a first stage and a first head,followed by heating for a first predetermined period of time whileexerting a first predetermined press load onto said first head tosemi-cure said first adhesive; applying a second adhesive to an actuatorbase; placing a base electrode on said second adhesive; clamping saidactuator base and said base electrode between a second stage and asecond head, followed by heating for a second predetermined period oftime while exerting a second predetermined press load onto said secondhead to semi-cure said second adhesive; applying a third adhesive tosaid base electrode; placing a piezoelectric element on said thirdadhesive; clamping said actuator base, said base electrode and saidpiezoelectric element between said second stage and a third head,followed by heating for a third predetermined period of time whileexerting a third predetermined press load onto said third head tosemi-cure said third adhesive; applying a fourth adhesive to saidpiezoelectric element; placing said movable electrode on said fourthadhesive; and clamping said actuator base, said base electrode, saidpiezoelectric element, said movable electrode and said movable platebetween said second stage and a fourth head, followed by heating for afourth predetermined period of time while exerting a fourthpredetermined press load onto said fourth head to semi-cure said fourthadhesive.
 6. A method of producing a micro-actuator as set forth inclaim 5, wherein said first to fourth adhesives comprise athermo-setting epoxy resin.
 7. A method of producing a micro-actuator asset forth in claim 5, wherein said first to fourth adhesives are appliedby use of a plurality of pins.
 8. A method of producing a micro-actuatoras set forth in claim 5, further comprising the step of heating theadhered laminate at a predetermined temperature for a fifthpredetermined period of time to fully cure said first to fourthadhesives.